In‐Season Nitrogen Status Sensing in Irrigated Cotton

Abstract

Nitrogen recommendations for Upland cotton (Gossypium hirsutum L.) in the western USA are based on spring soil NO−3–N tests. In‐season monitoring of plant N status is another approach. Our primary objective was to test spectral reflectance and chlorophyll meter measurements as in‐season N decision aids for irrigated cotton, and to compare these with soil test‐based N management. The secondary objective was to determine the fate of 15N as affected by N management and irrigation modes. Urea ammonium nitrate was applied with low energy precision (LEPA) center‐pivot, surface drip, and subsurface drip irrigation. Microplots received 3 atom% 15N. Soil test N application was based on 0‐ to 60‐cm soil NO−3–N and 1400 kg lint ha−1 expected yield. Thirty‐four kilograms of N per hectare was applied when green vegetative index (GVI) or chlorophyll meter readings relative to well‐fertilized plots were <0.95. Lint yield responded to N at Lubbock in 2000 and 2001, but not at Ropesville. Nitrogen applied with in‐season monitoring in 2000 at both sites was 34 to 101 kg N ha−1 less than soil test N application of 134 kg ha−1, with similar yields. In Lubbock, 2001 lint yields were near the expected yield, and in three of four cases, N applications with in‐season monitoring equaled soil test N applications of 101 kg ha−1 Nitrogen‐15 recovery in plants ranged from 19 to 38%, and was affected by N management in two of three site‐years, but not by irrigation. This study indicates that basing N applications on in‐season monitoring can reduce N applications in low yielding seasons and match the yield potential in high‐yielding seasons.

Effects of fertigation scheme on N uptake and N use efficiency in cotton

“…The recovery of 15 N fertilizer in plant ranged from 23 to 31% between the four fertigation schemes. Those values are within the range of plant 15 N recoveries previously reported for cotton (Freney et al 1993;Rochester et al 1993Rochester et al , 1997Torbert and Reeves 1994;Karlen et al 1996;Chua et al 2003). It is interesting to note that plant recovery was higher than the recovery of fertilizer N in soil in N-W treatment, but recovery of 15 N fertilizer in the soil was higher than plant recovery in other treatments.…”

Effects of salinity and fertigation practice on cotton yield and 15N recovery

“…The total 15 N recovery under different treatments ranged from 46% to 66% with an average of 54%. These values were within the range of total recovery of 15 N in plants and soils reported by other studies for irrigated cotton (Freney et al, 1993;Rochester et al, 1994;Torbert and Reeves, 1994;Karlen et al, 1996), but were smaller than those reported by Chua et al (2003) and Fritschi et al (2004). The result showed that on average, more than 40% of the applied N was unaccounted from the soil-plant system during the growing season.…”

“…Their results suggested that the impact of fertigation strategy on nitrate leaching was limited and nitrate leaching was not very significant under drip irrigation. Denitrification in soil wet zones therefore appears to be the highest possibility as a loss pathway (Thompson et al, 2000;Chua et al, 2003). This has been reported for irrigated cotton fields in Australia, where 43-63% loss of the applied N fertilizer was attributed mainly to denitrification (Freney et al, 1993;Chen et al, 1994).…”

“…These values are similar to those reported by Rochester et al (1994) for cotton. Chua et al (2003) reported that plant 15 N recoveries ranged from 19% to 38%…”

The relationship between N2O, NO, and N2 fluxes from fertilized and irrigated dryland soils of the Aral Sea Basin, Uzbekistan

“…Scheer et al 2008b and identified denitrification as the main pathway of fertilizer losses from the soilplant system (Chua et al 2003;Hou et al 2007). For irrigated cotton only limited information is available on gaseous N emissions and denitrification losses.…”